1. Field of the Invention
The present invention relates to a semiconductor integrated circuit.
2. Description of the Related Art
A technique of activating an instrument only when a human body is present near the instrument by mounting a sensor for detecting the presence of the human body in the instrument has been known in view of energy saving. Examples of the sensor mounted in the instrument include techniques of infrared sensors that quantitate the amount of energy emitted from the human body and entering the sensor, and detect the temperature of the human body. The instrument used herein is, for example, electric appliances and office machines.
The types of infrared sensors include a thermal infrared sensor, a quantum infrared sensor, and the like. The thermal infrared sensor converts infrared energy into thermal energy on an absorption face of the sensor, and detects a change in temperature as an electric signal. An output value VS of the thermal infrared sensor satisfies the following equation (1) in terms of the relation between an object temperature (for example, temperature of the human body) TA and a temperature TS of the infrared sensor. Here, U is a constant determined based on characteristics of the infrared sensor.VS=U(TA4−TS4)  (1)
As represented by the equation (1), to calculate the object temperature from the output value of the thermal infrared sensor, the temperature of the infrared sensor must be measured.
Thus, it is necessary to measure the temperature of the infrared sensor, and then to calculate the object temperature by using the output value of the infrared sensor and the measured temperature of the infrared sensor.
A temperature measuring device including an infrared sensor and a temperature measuring unit for measuring the temperature of the infrared sensor has heretofore been proposed (Refer to Japanese Unexamined Patent Application Publication No. 2012-78159, for example).
However, for the proposed temperature measuring device, calculating the object temperature requires solving a high-order polynomial expression having a large number of significant figures. For example, Japanese Unexamined Patent Application Publication No. 2012-78159 states that calculating the object temperature requires solving the following equation (2), where TAMB is an environmental temperature, and B is an offset correction value for correcting a measurement error of the environmental temperature.B=(−7.6885×10−6)×TAMB3−(1.5578×10−3)×TAMB2−(6.8163×10−2)×TAMB+3.7461  (2)
However, solving such high-order polynomial expression having a large number of significant figures makes an arithmetic circuit complicated and larger in scale, increasing the area of an integrated circuit and in turn, manufacturing costs, for the calculation on the integrated circuit.